The present invention is directed to a carbonless paper which can be employed in electrophotographic imaging processes. More specifically, the present invention is directed to a carbonless paper set having at least two sheets, wherein a first sheet comprises paper coated on one surface with a color former, and a second sheet comprises paper coated on one surface with a color developer, and wherein at least one of the sheets contains an oleophilic pigment on the surface of the sheet opposite to that coated with the color former or color developer. One embodiment of the present invention is directed to a carbonless paper set which comprises a first sheet comprising a first paper support comprising paper fibers, said first paper support being coated with a color former, and a second sheet comprising a second paper support comprising paper fibers, said second paper support being coated with a color developer, wherein at least one of the paper supports contains an oleophilic pigment filler material within the paper fibers. Another embodiment of the present invention is directed to a carbonless paper set which comprises a first sheet comprising a first paper support comprising paper fibers, said first paper support being coated with a color former, and a second sheet comprising a second paper support comprising paper fibers, said second paper support being coated with a color developer, wherein at least one of the paper supports contains an oleophilic pigment filler material coated onto the surface of the support opposite to the surface coated with the color former or color developer.
Carbonless paper sets generally are stacks of at least two sheets of paper wherein the application of pressure in imagewise fashion on the top sheet, typically by handwriting or typing, results in formation of a corresponding image on the underlying sheets, so that copies are formed as the image is generated on the top sheet. Carbonless paper sets typically comprise a top sheet of paper, on the bottom surface of which is coated a first composition, and a bottom sheet, on the top surface of which is coated a second composition. The first and second compositions are in contact with each other when the top and bottom sheets are placed in stack formation, and generally are of a nature such that application of pressure to the top sheet of the stack at a specified location causes interaction between the first and second compositions that results in the formation of a colored area on the bottom sheet at the location at which pressure was applied. Intermediate sheets can be located between the top and bottom sheets, wherein each intermediate sheet is coated on its top surface with the second composition and on its bottom surface with the first composition; application of pressure to the top sheet then results in the formation of a colored area at the location at which pressure was applied on each of the intermediate sheets and on the bottom sheet.
An example of a carbonless paper set is disclosed in U.S. Pat. No. 3,843,383, the disclosure of which is totally incorporated herein by reference. This patent discloses a recording sheet comprising a support having thereon a layer of color developer capable of reacting with a substantially colorless color former to form colored images. The paper set generally comprises a top sheet coated with microcapsules containing a color former solution, a bottom sheet coated with a color developer material in a binder, and, in some instances, middle sheets coated on one surface with the color developer and on the other surface with the color former microcapsules. Contacting a top sheet coated with color former containing microcapsules on its bottom surface with a bottom sheet coated on its top surface with a color developer and applying pressure to the paper "sandwich" thus formed results in formation of a color image. Other patents disclosing carbonless paper of this type include U.S. Pat. No. 2,712,507 and U.S. Pat. No. 2,730,456, the disclosures of which are totally incorporated herein by reference. Alternatively, as disclosed in U.S. Pat. No. 2,730,457, the disclosure of which is totally incorporated herein by reference, the color former microcapsules and the color developer of a carbonless paper can be applied to the same surface of a paper sheet. Other configurations of color former, color developer, and a pressure-releasable liquid solvent are possible, including, for example, those disclosed in U.S. Pat. No. 3,672,935, the disclosure of which is totally incorporated herein by reference. Additional patents disclosing carbonless papers and materials suitable for carbonless paper applications include U.S. Pat. No. 2,417,897, U.S. Pat. No. 3,672,935, U.S. Pat. No. 3,681,390, U.S. Pat. No. 4,202,820, U.S. Pat. No. 4,675,706, U.S. Pat. No. 3,481,759, U.S. Pat. No. 4,334,015, U.S. Pat. No. 4,372,582, U.S. Pat. No. 4,334,015, U.S. Pat. No. 2,800,457, U.S. Pat. No. 2,800,458, U.S. Pat. No. 3,418,250, U.S. Pat. No. 3,516,941, U.S. Pat. No. 4,630,079, U.S. Pat. No. 3,244,550, U.S. Pat. No. 3,672,935, U.S. Pat. No. 3,732,120, U.S. Pat. No. 3,843,383, U.S. Pat. No. 3,934,070, U.S. Pat. No. 3,481,759, U.S. Pat No. 3,809,668, U.S. Pat. No. 4,877,767, U.S. Pat. No. 4,857,406, U.S. Pat. No. 4,853,364, U.S. Pat. No. 4,842,981, U.S. Pat. No. 4,842,976, U.S. Pat. No. 4,788,125, U.S. Pat. No. 4,772,532, and U.S. Pat. No. 4,710,570, the disclosures of each of which are totally incorporated herein by reference.
Often, carbonless papers are passed through mechanical devices that include automated paper handling systems. Such devices include printers, copiers, and duplicators for imprinting information on the carbonless sheets, as well as automatic sorting devices such as magnetic card readers and Optical Character Recognition devices for reading coded information from the carbonless sheets. All such devices contain pressure nips, including, for example, those between elements of the paper transport system such as feed belts and wheels, retard rollers, pinch rollers, and the like. When carbonless paper is passed through these devices, these elements come into contact with the surfaces of the carbonless sheets, and often become contaminated with components of the carbonless color forming coating, color developer coating, or both, which may produce a deleterious effect on the continued operation of the device. In particular, the microcapsules of the carbonless color former layer can become ruptured in a pressure nip, causing the color former solution to be deposited on one or both elements of the nip. This material may interact with other components of the carbonless coatings, or with components of other throughput materials, causing contamination and failure of the device.
For example, frequently, it is desirable to generate images on carbonless paper sets in electrophotographic copiers and duplicators. In such instances, each sheet of paper in a stack is fed sequentially into the imaging apparatus, wherein an electrostatic latent image of one polarity is formed on an imaging member. The image is then developed with a toner charged to a polarity opposite to that of the latent image, and the developed image is transferred to the paper. Transfer is frequently effected by applying an electric charge of the same polarity as the latent image (and opposite of the polarity on the toner particles) to the back of the paper sheet. The charge applied to the back of the sheet is of greater magnitude than the charge of the latent image, which results in the toner particles becoming attracted to the paper and thus transferred from the imaging member to the paper. The charge may be applied in a non-contact manner by an ion deposition device, such as a corotron, scorotron, or similar device, or by contacting the back of the sheet by a charged roller conventionally known as a bias transfer roller. When a bias transfer roller is used, the paper passes through a nip formed between the imaging member and the bias transfer roller. After transfer to the paper, the image is generally fused to the paper by conventional methods, such as application of heat, pressure, or the like. Subsequent to fusing, the stack is reassembled so that the sheets are in their proper sequence in the stack.
When carbonless paper sets are passed through copiers and duplicators, frequently a problem arises with contamination of the imaging member with tackified clusters of toner. As the carbonless paper sheets pass through the imaging device, portions of the color former composition coating the paper sheets become transferred onto the imaging member, either as a result of direct contact between the imaging member and the coated paper, or indirectly as a result of contact between the coated paper and the bias transfer roll and subsequent contact between the bias transfer roll and the imaging member, which are in intimate contact prior to and subsequent to the passage of a sheet between them. Toner particles then accumulate on areas of the imaging member where portions of the coating composition are located and become tackified, thus contaminating the imaging member. Similar difficulties with contamination can occur at other pressure nips in an imaging device, such as that formed by contact between paper feeding components, or that formed by two fuser rolls. Similar contamination problems can also occur at pressure nips in other mechanical devices with automated paper handling systems.
U.S. Pat. No. 4,906,605, the disclosure of which is totally incorporated herein by reference, discloses a carbonless copy paper for imaging via electrostatic copiers comprising a paper stock having a basis weight greater than about 18 pounds per ream and containing on at least a portion of a surface thereof a stilt particle-free composition comprising microcapsules, at least 50 volume percent thereof having a size no greater than about 12 microns and at least 95 percent by volume thereof having a size no greater than about 18 microns. The reference discloses reduced contamination of the bias transfer roll and imaging member in an electrophotographic device by carbonless color former sheets with a coating of microcapsules within the disclosed particle size range. By eliminating larger sized microcapsules which are most prone to breakage, the amount of solvent oil released in the pressure nip between the transfer roll and imaging member is reduced. This approach, however, cannot totally eliminate solvent oil contamination of the imaging member, since on each carbonless color former sheet, a number of microcapsules will have been broken during manufacture of the sheet (during either the coating or sheeting operations), or during subsequent packaging, transportation, and handling of the finished product, or during feeding and transport of the sheet into the electrophotographic device. Solvent oil from such inadvertently ruptured microcapsules is still available to cause contamination of the bias transfer roll and imaging member.
In addition, U.S. Pat. No. 4,398,954, the disclosure of which is totally incorporated herein by reference, discloses a coating composition comprising oil-containing microcapsules dispersed in an aqueous continuous phase, which phase also contains finely divided silica particles and a binder for the microcapsules and silica particles. The silica particles have been treated with an organic material such as an organic silicon compound to give the particles a hydrophobic surface. The coating composition can be used in the manufacture of paper coated with microcapsules. The paper is characterized by a substantial reduction of specking when used in photocopying apparatuses using a pressure nip to assist transfer of a powder image from a photoreceptor belt to paper. In a preferred embodiment, the coated paper is used in the production of multipart forms. The reference discloses reduced contamination of the bias transfer roll and imaging member of an electrophotographic device by means of incorporating finely divided silica particles and a binder along with microcapsules in a carbonless color former coating. The silica particles are apparently intended to absorb the solvent oil from inadvertently ruptured microcapsules before it can transfer to the bias transfer roll or imaging member. However, there is a limit to the amount of solvent oil that can be absorbed in the color former coating without impairing the image forming capabilities of the carbonless set. By its nature, a carbonless color former sheet must be able to release from its surface substantial amounts of color former dissolved in solvent oil, which can then transfer to the color developing sheet where the color former and color developer react to form the carbonless image.
The present invention reduces or eliminates these problems by providing a carbonless paper set that is "self-cleaning". Incorporated during manufacture into the base paper of the top sheet, the bottom sheet, or both the top and bottom sheets of the carbonless paper stack of the present invention is a pigment material that tends to absorb rapidly the coating material that has been transferred to the upper or lower elements of a pressure nip through which the carbonless paper has been passed, such as, for example, the imaging member of the bias transfer roll in an electrophotographic imaging device. Thus, when the carbonless paper stack is fed sequentially into the imaging device, an uncoated surface of the paper containing the pigment material contacts the imaging member, the bias transfer roll, or both, thereby absorbing the coating material, typically a carbonless oil, on the imaging member or bias transfer roll and removing it therefrom. Since the coating material is periodically removed by the oil absorbing pigment material in the "self-cleaning" paper either from the imaging member and/or the transfer roll, contaminating accumulations of tackified toner deposits do not form on the imaging member. A similar self-cleaning process occurs at other pressure nips in the imaging device, or at pressure nips in other devices, thus also reducing contamination at these sites.
U.S. Pat. No. 4,046,404, the disclosure of which is totally incorporated herein by reference, discloses a carbonless paper suitable for use in electrostatographic copiers. The paper comprises a base sheet of paper making fibers having uniformly dispersed therein from about 0.05 to 10 percent by weight of hollow, generally spherical particles ranging in diameter from about 1/2 to 200 microns in diameter. These particles serve the purpose of increasing the stiffness and caliper of the paper sheet. The carbonless paper also contains a color forming material encapsulated in discrete particles and/or a color developing material.
The incorporation of oleophilic pigments into paper in general is known. For example, U.S. Pat. No. 2,935,438, the disclosure of which is totally incorporated by reference, discloses a process for incorporating fillers and pigments into paper. Incorporation of the filler or pigment is intended to impart improved physical and optical properties to the paper, increase the volume or bulk of the paper, impart to the paper opacity, brightness, or color, and result in good surface smoothness, absorption, and ink receptivity of the paper. The process entails reacting precipitated hydrated calcium silicate with aluminum sulfate in an aqueous medium so that at least 50 percent of the calcium silicate is in the solid phase to form a finely divided insoluble reaction product of the calcium silicate and the aluminum sulfate. The insoluble product may then be added to the pulp slurry during manufacture, or it may be later applied to the formed paper sheet.
In addition, U.S. Pat. No. 2,249,118, the disclosure of which is totally incorporated herein by reference, discloses a soft, flexible, durable paper which may be used in the manufacture of articles commonly made of textile fabrics. The paper retains its softness and durability whether wet or dry, and can be cut and sewn like cloth. These characteristics are obtained by incorporating into the paper a sizing material consisting essentially of softening agents, such as glycerine or other stable water soluble liquids with a higher boiling point than water, dissolved in water, and a water insoluble mineral filler, which filler fixes or anchors the softening agent in the paper so that it will not dissolve or evaporate. The filler materials act as adsorbents to retain the softening agent in the paper and distribute it throughout the paper. Suitable fillers include calcium, magnesium, and aluminum oxides, aluminum silicates such as kaolin, fuller's earth, and pumice, and silicates, carbonates, sulfates, and fluorides of calcium and magnesium.
Further, U.S. Pat. No. 4,580,152, the disclosure of which is totally incorporated herein by reference, discloses a method for carrying out heat sensitive transfer which comprises using a transfer sheet having a leuco dye-containing transfer layer and a receiving sheet having a receiving layer containing a bisphenol-system compound and a porous filler whose oil absorption is 50 ml/100 g or more and bringing the transfer sheet into contact with a thermal head. Examples of porous fillers include inorganic fine powders of silica, aluminum silicate, alumina, aluminum hydroxide, and magnesium hydroxide, and organic fine powders of urea-formalin resin and styrene resin, with a particle diameter of 0.01 to 10 microns.
Additionally, U.S. Pat. No. 3,801,433 discloses a process for reducing the deposition of pitch during paper manufacturing by adding to the pulp from which paper is to be made a quantity of a clay pigment which has been coated with an organic material that adheres strongly to the clay pigment and that renders the surface of the pigment particles oleophilic. The organic material generally is an organic amine, its water-soluble salt, its reaction product with alkylene oxides, an alkyl pyridinium salt, a quaternary ammonium salt, or a mixture thereof, and is applied to the clay pigment in an amount of from 0.5 to 5 percent by weight of the pigment. One suitable clay pigment is kaolinitic clay. The coated pigment is added to the pulp during paper manufacture, and reduces deposition of pitch during manufacture.
Other references disclosing the use of pigments and clays in paper include U.S. Pat. No. 2,368,635, the disclosure of which is totally incorporated herein by reference, which discloses a method of forming a sheet of paper or a ply of paperboard from a dilute suspension of fibers. Preferably, a preformed aluminum silicate mineral is applied to the fiber suspension. The aluminum silicate physically separates the fibers in water so that a more uniform distribution is obtained. In addition, U.S. Pat. No. 2,599,094, the disclosure of which is totally incorporated herein by reference, discloses paper containing a cellulosic fiber and calcium silicate pigment. The pigment comprises highly pigmented cellulosic pulp fibers containing finely divided hydrated calcium silicate precipitated largely within the fibers and on and around the fibers in an amount greatly exceeding the weight of the fibers. Further, U.S. Pat. No. 2,786,757, the disclosure of which is totally incorporated herein by reference, discloses a process for preparing a paper product with high brightness and opacity by forming a paper pulp dispersion in an aqueous acidic material which forms a substantially water-insoluble salt of an alkaline earth metal and adding calcium silicate or an equivalent alkaline earth metal silicate to the acidic slurry. U.S. Pat. No. 2,786,758, the disclosure of which is totally incorporated herein by reference, discloses a process for preparing paper containing a siliceous pigment. The pigment is prepared by reaction of an alkaline earth metal silicate such as calcium silicate with aluminum sulfate in an aqueous medium initially containing an alkaline earth metal sulfate such as calcium sulfate. Paper of high whiteness and brightness is prepared by adding to a slurry of paper forming fibers a quantity of aluminum sulfate and, after the aluminum sulfate solution has permeated the pores of the slurry, adding a quantity of calcium silicate. Additionally, U.S. Pat. No. 2,888,377, the disclosure of which is totally incorporated herein by reference, discloses a process for producing calcium silicate, which can be used as an opacifier, reinforcing pigment, or loading agent for paper. Further, U.S. Pat. No. 2,919,222, the disclosure of which is totally incorporated herein by reference, discloses a process for making paper wherein finely divided, hydrated calcium silicate pigment is added to a furnish comprising pulp, sizing material, filler, and other ingredients to form paper containing the pigment.
U.S. Pat. No. 4,636,410, the disclosure of which is totally incorporated herein by reference, discloses the preparation of various pigmented coating formulations used for producing highly absorbent recording papers. Additionally, U.S. Pat. No. 4,440,827, the disclosure of which is totally incorporated herein by reference, discloses coatings based upon highly absorbent inorganic pigments dispersed in various aqueous organic binder systems. U.S. Pat. No. 4,478,910, the disclosure of which is totally incorporated herein by reference, describes the application of various high surface area pigment-based formulations to base papers with a specific degree of hydrophobic sizing, to produce highly absorbent recording papers with more plain-paper like tactile properties. In addition, U.S. Pat. No. 4,734,336, the disclosure of which is totally incorporated herein by reference, discloses the preparation of highly absorbent papers based on a multi-ply structure, whereby the outer-ply incorporates various concentrations of highly absorbent oleophilic pigments.
In addition, the incorporation of oil absorbent pigments in carbonless papers is known. For example, U.S. Pat. No. 4,154,462, the disclosure of which is totally incorporated herein by reference, discloses a transfer sheet having a substrate coated with pressure-rupturable microcapsules containing an oil and an oil-soluble dye intermediate and a particulate oil-absorptive material which is non-reactive with the dye intermediate and is situated with respect to the microcapsules such that oil released by the microcapsules is absorbed thereby. The concentration of oil absorptive material is sufficient to permit writing on the coated substrate without interference from oil released by ruptured microcapsules but less than that which materially reduces the transfer of oily solution from ruptured microcapsules to an underlying copy sheet. Also, U.S. Pat. No. 3,481,759, the disclosure of which is totally incorporated herein by reference, discloses self-marking papers of the transfer or manifolding type that operate by having a dye precursor within microscopic capsules carried as a transfer coating on one sheet of paper, the dye precursor within the capsules reacting with a receptor coating on a mating sheet of paper to produce a visible mark on the mating sheet upon impact against the contacting transfer and receptor coatings when the two sheets of paper are mated, the microcapsules at the point of impact rupturing and releasing their contents onto the receptor coating of the mating sheet. To prevent the inadvertent marking or backgrounding during handling, a co-reactant for the dye precursor is included in the transfer coating containing the capsules but externally of the capsules so that upon the inadvertent rupture of capsules in the transfer coating the contents will react with the colorless co-reactant before passage through the sheet or transfer to the receptor sheet coating, and thus prevent inadvertent marking of the paper. Scuff capsules to help further prevent inadvertent marking may also be included in the transfer coating along with the dye precursor containing capsules. Further, U.S. Pat. No. 4,089,547, the disclosure of which is totally incorporated herein by reference, discloses manifold receptor sheets for use with conventional donor sheets, the receptor sheet comprising a substrate having deposited thereon a coating comprising hydrophobic fumed silicon dioxide, together with processes for producing such receptor sheets. The reference discloses a carbonless color developer coating consisting of very small particles (7 to 14 nanometers in diameter) of hydrophobic fumed silicon dioxide and a suitable binder. The particles of silicon dioxide have a surface area of from 200 to 400 square meters per gram.
Of additional background interest are U.S. Pat. No. 2,929,736, which discloses a heat and pressure responsive record material in which a microencapsulated color former solution and a color developing pigment are combined in a single coating; U.S. Pat. No. 2,980,941, which discloses a soil-removing sheet consisting of encapsulated soil-removing solvent along with an absorptive material such as Fuller's earth; and U.S. Pat. No. 3,776,864, which discloses a transfer ink containing a dye and a filler to prevent the coating from having a greasy surface.
U.S. Pat. No. 4,554,181 discloses an ink jet recording sheet having a recording surface which includes a combination of a water soluble polyvalent metal salt and a cationic polymer, said polymer having cationic groups which are available in the recording surface for insolubilizing an anionic dye. The recording surface may be formed by applying an aqueous solution of the aforesaid salt and polymer to the surface of an absorbent sheet material such as paper or by applying a coating containing the polymer and salt combination alone or in combination with a binder to the surface of a substrate.
In addition, U.S. Pat. No. 4,792,487 discloses an ink jet printing substrate particularly useful as a coating for multi-color, water base ink jet printing. The substrate consists essentially of a high swelling montmorillonite clay and optionally includes a high surface area pigment such as synthetic silica or calcium carbonate and a water-insoluble binder.
Further, U.S. Pat. No. 4,778,711 discloses an electrophotographic image transfer paper for a copier including a fixing operation which comprises a sheet of raw paper and a receiving layer on the paper for reducing blistering of the sheet during fixing of an image on the sheet. The receiving layer includes a coating on at least one side of the sheet having a center-line-average surface roughness of not more than 2.0 micrometers and an air permeability less than or equal to 4,000 seconds. The coating comprises water soluble adhesives and pigments that have small particle sizes and high levels of oil absorption.
Copending application U.S. Ser. No. 07/616,971, the disclosure of which is totally incorporated herein by reference, discloses a process for generating images which comprises incorporating into an ink jet printing apparatus a carbonless paper set which comprises a first sheet comprising a support containing a color developer capable of reacting with a color former to produce a color image, said color developer comprising high surface area silica particles, and a second sheet comprising a support coated with the color former, forming an image on the first sheet by causing ink to be expelled in droplets on the surface containing the color developer, and forming an image on the second sheet by causing ink to be expelled in droplets onto the surface opposite to that coated with the color former.
Although the known compositions and processes are suitable for their intended purposes, a need remains for a carbonless paper that is suitable for use in electrophotographic printers, copiers, and duplicators. In addition, a need exist for carbonless paper that will not contaminate imaging members in printers, copiers, and duplicators. Further, there is a need for carbonless paper that enables removal of residual coating materials from various components of an imaging device as it passes through the device. Further, there is a need for carbonless paper that enables removal of residual coating materials from pressure nips in various mechanical devices incorporating automated paper handling systems. Additionally, a need remains for a process of generating images on the sheets of a carbonless paper set wherein residual coating material from the coated sheets is periodically removed from components of the imaging device that contact the coated sheets. There is also a need for carbonless paper that is compatible with imaging apparatuses employing bias transfer rollers.